Diplodocus lived during the Late Jurassic period, Diplodocus lived in Western North America. The trees helped Diplodocus lived, Diplodocus was the longest than all the dinosaurs. Diplodocus was a sauropod, Diplodocus was a herbivore. That means it eat leaves, the first Diplodocus fossil was found by Earl Douglass and Samuel W. Many Diplodocus fossils have been found by the Rocky Mountains on the Western United States of America, (Montana, Utah, Wyoming and Colorado).